Single-chip ASIC/ASSP Solutions Power Innovation In Medical Devices

Medical device technology is advancing at a rapid rate allowing the delivery of better and less intrusive patient care. This is being fuelled by semiconductor design advances that are delivering smaller form factor solutions able to combine analog circuits and digital signal processing in a single device.

A growing number of implantable medical devices are also integrating ultra-low power medical implant communication service (MICS) based radios. This is taking implanted devices to another level where data collected and processed by the implant can be wirelessly transmitted to the outside world providing useful, often critical information to medical professionals.

The challenges presented to the designers and manufacturers of semiconductors for medical applications are tough and ongoing as the quest for smaller form factors, lower power consumption and greater functionality continues. Making the challenge harder is the pre-requisite of extreme reliability and the inevitable demand for low cost.

Applications
The number of medical applications for semiconductors is increasing as more biomedical equipment classes take advantage of what single chip, small form factor, mixed signal electronics have to offer. For example, being able to combine analog and digital signals in very close proximity alongside wireless communication has enabled the development of new implantable cardiac rhythm management (CRM) products, neurostimlutators, drug pumps, and glucose and pressure sensors.Outside the body, similar technology has facilitated the design and manufacture of a new generation of digital hearing aids that offer far superior performance compared to their analog predecessors. These are housed in packages so small that they can be fitted discreetly into the ear canal.

New process technologies
All single chip ASIC/ASSP (application specific integrated circuit) solutions for implantable medical applications are required to consume as little power as possible in order to extend battery life and therefore lengthen the time between invasive replacement procedures. However, in many applications there is an additional challenge – that while achieving the lowest possible power consumption, the ASIC/ASSP must also be capable of delivering high voltage signals; In CRM applications control output stages are likely to involve voltages ranging from 10V for pacemakers to almost 1000V for defibrillators. In the past, the conflicting requirements of low power and high voltage have meant that two different chips had to be developed. Application size constraints have proved the key driver in forcing the two chips together, requiring new manufacturing processes to be developed that allow low power and high voltage to coexist in a single device.

AMIS has addressed the problem by using a special isolation scheme called a deep trench barrier that physically separates on-chip low power circuits from the high power voltages. The deep trench barrier is added to a modified version of a CMOS semiconductor manufacturing process that is commonly used in medical electronics.

Adding low power radio
With the MICS band radio standard now well established, the number of implantable devices that include a low power radio transmitter or transmitter / receiver is rapidly increasing. As well as allowing the download of recorded data, low power radio also facilitates the reprogramming of implanted devices. In the case of CRM devices, radio frequency (RF) communication is expected to replace the established but cumbersome inductive-sensing technology currently employed.

The relatively low data rate (between 10kbits/s and 20kbits/s) and short-range requirements of medical applications make relatively small demands on power. However, with any extension to the effective life of an implanted device considered a benefit, semiconductor companies have taken additional steps to further reduce power consumption. AMIS, for example, uses a feature called ‘sniff mode' whereby the radio is normally in sleep mode only waking periodically to poll the appropriate radio frequency for the presence of an inquiring RF signal. The acquisition poll frequency can be pre-set to suit the needs of a specific application.

Conclusion
The number of applications and use of single chip solutions for implantable and other medical devices looks set to continue increasing. The availability of numerous analog and digital IP building blocks will help reduce development time and costs and simplify the implementation of the technology into medical applications. The inclusion of low power radios into implanted devices will allow patients to be wire-free giving them a better quality of life whilst providing medical staff easy access to more data than has been possible in the past.

SOURCE: AMI Semiconductor